This invention relates to a snap action switch. The invention is more particularly related to an improved snap action assembly within the switch that minimizes the failure rate of the snap action switch due to the minimizing of stresses within a metallic member that previously caused breaking or failure of the switch.
Snap action switches, though simple in construction, possess excellent performance characteristics. Examples of such switches are disclosed in U.S. Pat. No. 2,805,297 entitled "Snap Switch Mechanism" issued on Sept. 3, 1957 to G. J. Campbell and U.S. Pat. No. 3,335,240 entitled "Snap Action Switch Device With Improved Circuit Breaker Mechanism", issued Aug. 8, 1967 to E. Dhaens et al. Snap switches of this general type have been employed in a wide variety of circuit control applications. The switches normally include a leaf spring blade provided with a longitudinal slot which extends from one end of the point short of the other end. Bifurcated arms, defined by the slot, are drawn together to stress the blade for snap action. With one end of such blade fixedly mounted, the free extending end normally rests in stable equilibrium at a selected off-center position. By applying pressure at an appropriate point on the blade, near the slot, the free end of the blade may be made to snap from the previously stable position to a new position.
In a simple single-pole, normally open snap action switch, it has been a conventional practice to affix one contact to a snap action blade. Another contact, engageable with the first contact, is located in a shaft so that when pressure is applied to the stressed blade, it snaps the two contacts together under substantial pressure to close an electrical circuit. The snap-action is normally accompanied by an audible "click" which serves to notify the operator of the switch that circuit closure has been accomplished.
When the applied pressure is removed, the stressed blade snaps to its original stable position. The snapping action is accompanied by considerable hysteresis -- that is, once sufficient pressure has been applied to cause the blade to be snapped out of its normal stable position, considerably less pressure is required to hold the blade in the new position. As pressure is slowly released, the extended end of the blade may move slightly and open the contacts before the blade makes the return of the original position. This effect, termed "switch teasing" constitutes a serious disadvantage in many applications. Because of this teasing effect, partial release of applied pressure due to inadvertence may open the circuit without causing the switch to snap back to its original position. Misled by the absence of a return "click" the operator may well believe that a circuit continues to be energized. When snap switches are used in a critical application, such as aviation control circuits, the failure to provide positive notification of a circuit opening constitutes a particularly serious disadvantage. In addition, the gap width between the contacts of a teased switch may be quite small. This condition may cause serious arcing across the narrow air gap, resulting in damage to the contacting surfaces.
To eliminate the aforementioned problems, snap action switches have been designed wherein one portion of the leaf spring member carrying the electrical contact was folded over so that a snap action blade having its free end would extend into the gap formed by the fold in the leaf spring. The gap was substantially wider than the width of the snap action blade to permit substantial movement of the blade, between the opposing surfaces of the fold which defied the gap, without causing any motion of the contact carrying leaf spring member. This approach eliminated teasing by allowing substantial movement of the snap action blade before the contacts were separated. However, the fold in the leaf spring member, which was comprised of metal (spring steel), was about 180.degree.. This resulted in undue stresses and strains in the metal comprising the curvature in the fold. The stresses and strains within the fold eventually led to failure of the switch or a large amount of unusable leaf spring members when the leaf spring was formed because the folding causes breaking and cracking of the leaf spring member. Similar problems are present when the fold is attempted to be made in the snap action blade which is comprised of spring steel.